1. Field of the Invention
The present invention generally relates to a semiconductor device, and more particularly, to a semiconductor device dealing with a high-frequency signal including a microwave.
Conventionally, a ceramic package has been mainly used as a package for a semiconductor device dealing with a microwave. Recently, however, a resinous package has been put to use even for such a semiconductor device dealing with a microwave. Additionally, such a semiconductor device dealing with a microwave, which per se has become highly multifunctional and operative at high speed, requires a package suitable therefor.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 1-202853 discloses a high-frequency-adapted mold-package semiconductor device in which impedances of an exposed portion and an unexposed portion of a lead are matched. This semiconductor device is a semiconductor device of a small outline package (SOP) type in which the lead extends from a side surface of a resinous package portion.
In the above-mentioned semiconductor device, a characteristic impedance of the exposed portion of the lead (a part extending from the resinous package) and a characteristic impedance of the unexposed portion of the lead (a part embedded in the resinous package) are matched by adjusting a form or an arrangement of the lead so as to prevent a microwave from reflecting at a boundary part between the exposed portion and the unexposed portion.
Additionally, in a microwave-adapted semiconductor device, ground leads need to be provided at both sides of a lead used for a high-frequency signal. That is, providing external ground electrodes at both sides of an external electrode used for a high-frequency signal prevents an interference by the high frequency while keeping the semiconductor device small.
In the above-described semiconductor device disclosed in Japanese Laid-Open Patent Application No. 1-202853, the lead must have a complicated form so as to match the characteristic impedance of the exposed portion and the characteristic impedance of the unexposed portion.
In addition, upon connecting the above-described semiconductor device to a printed substrate, etc., differences in relative dielectric constants of materials composing the printed substrate cause a need for readjusting the characteristic impedances. For example, when the impedances are matched on the assumption that the semiconductor device is connected to a ceramic substrate, and thereafter the ceramic substrate is changed to an epoxy substrate, the impedances have to be readjusted.
Specifically, when the relative dielectric constant of the material composing the printed substrate contacting the exposed portion changes, the impedance of the exposed portion also changes so as not to match the impedance of the unexposed portion. Thereupon, in order to adjust the impedance of the exposed portion of the lead in consideration of the relative dielectric constant of the printed substrate, a lead frame per se needs to be redesigned.
Additionally, since the unexposed portion is surrounded by a sealing resin, the unexposed portion of the lead is affected by a characteristic of the sealing resin. Especially, with respect to a lead transmitting a microwave, a transmission characteristic becomes aggravated depending on a type of the sealing resin.
It is a general object of the present invention to provide an improved and useful semiconductor device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a semiconductor device in which an impedance of a lead is not affected by a material composing a mounting substrate, and an influence of a sealing resin to a transmission characteristic can be reduced.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a semiconductor device comprising:
a semiconductor chip;
a signal lead connected to a signal electrode of the semiconductor chip;
an external signal electrode connected with the signal lead;
a ground lead extending along the signal lead; and
a sealing resin sealing the semiconductor chip, the signal lead, the external signal electrode and the ground lead,
wherein the external signal electrode is formed as a protruding electrode protruding from an undersurface of the sealing resin, and one surface of the signal lead is exposed on the undersurface of the sealing resin.
According to the present invention, one surface of the signal lead is exposed on the undersurface of the sealing resin, and the external signal electrode is formed as a protruding electrode; therefore, when the semiconductor device is mounted on a mounting substrate, an air gap is formed between the signal lead and the mounting substrate. Thereby, the exposed signal lead does not contact the mounting substrate, and thus, an impedance of the signal lead does not change by being affected by a material forming the mounting substrate. Accordingly, even when the material forming the mounting substrate is changed, the same semiconductor device remains usable. In addition, since only one surface of the signal lead contacts the sealing resin, a signal transmission loss due to the sealing resin can be reduced, in comparison with a case in which both surfaces of the signal lead contact the sealing resin.
Additionally, the semiconductor device according to the present invention may further comprise a ground electrode provided under the semiconductor chip, the ground electrode protruding at a same height as the external signal electrode protrudes on the undersurface of the sealing resin.
According to the present invention, the semiconductor device can be connected to a mounting substrate, not only by the external signal electrode arranged in an outer peripheral part of the semiconductor device, but also by the ground electrode positioned under the semiconductor chip.
Additionally, in the semiconductor device according to the present invention, the ground electrode may be formed larger than an outer shape of the semiconductor chip, and a ground electrode of the semiconductor chip may be connected to the ground electrode by a bonding wire.
According to the present invention, the ground electrode of the semiconductor chip can be grounded to the ground electrode positioned nearby so as to achieve an excellent grounding effect.
Additionally, the semiconductor device according to the present invention may further comprise an external ground electrode adjacent to the external signal electrode.
According to the present invention, a part neighboring the external signal electrode can be grounded so as to achieve an excellent grounding effect.
Additionally, the semiconductor device according to the present invention may further comprise an outer peripheral ground portion provided in a periphery of the external signal electrode, wherein the ground lead extends along the signal lead from the ground electrode to the outer peripheral ground portion.
According to the present invention, peripheries of the signal lead and the external signal electrode are completely encompassed by the ground lead and the outer peripheral ground portion so as to achieve an excellent shield effect.
Additionally, in the semiconductor device according to the present invention, the ground electrode of the semiconductor chip may be connected to the ground lead by the bonding wire.
According to the present invention, a connecting point of the bonding wire can be changed along the ground lead so as to adjust a length of the bonding wire connected to the ground electrode.
In order to achieve the above-mentioned objects, there is provided according to another aspect of the present invention a semiconductor device comprising:
a semiconductor chip;
signal leads connected to signal electrodes of the semiconductor chip;
external signal electrodes connected with the signal leads;
at least one ground lead extending along only a signal lead transmitting a high-frequency signal, among the signal leads; and
a sealing resin sealing the semiconductor chip, the signal leads, the external signal electrodes and the ground lead,
wherein each of the external signal electrodes is formed as a protruding electrode protruding from an undersurface of the sealing resin, and one surface of each of the signal leads is exposed on the undersurface of the sealing resin.
According to the present invention, the ground lead is not provided for a signal lead not transmitting a high-frequency signal. Therefore, unnecessary ground leads are not formed, and thus a size of the semiconductor device can be reduced to that extent.
Additionally, in the semiconductor device according to the present invention, a characteristic impedance of the signal lead may be so adjusted that an input-output impedance of the semiconductor chip matches an impedance of an external circuit connected to the signal lead via the external signal electrode.
According to the present invention, a high-frequency signal can be efficiently supplied from the external circuit to the semiconductor chip.
Additionally, in the semiconductor device according to the present invention, the characteristic impedance may be adjusted by adjusting a wire diameter of each of bonding wires connected to the signal electrode and a ground electrode of the semiconductor chip and adjusting an interval between the bonding wires.
According to the present invention, a high-frequency signal can be efficiently supplied from the external circuit to the semiconductor chip.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.